1. Field of the Invention
This invention relates generally to the field of regenerative gas or air drying systems and more particularly to such regenerative gas or air drying systems which employ a desiccant contained in a chamber to adsorb moisture of the wet gas inserted into the chamber to dry the gas and in which dry purge gas is subsequently inserted into the chamber to regenerate saturated desiccant which had absorbed the moisture in drying the previously inserted wet gas.
2. Description of the Related Art Including Information Disclosed Under 37 C.F.R. .sctn.1.97-1.99
Drying devices which receive a wet gas under pressure such as air containing a high level of moisture are well known. These gas drying devices are commonly used in many industrial applications such as spray painting, pneumatic control systems and air operated equipment. It is also known in such devices to utilize a desiccant such as activated alumina, carbons, silica gels or molecular sieves located in a chamber to adsorb and remove the moisture from the inlet inserting the wet air under pressure to one end of the chamber. Such air drying devices frequently use a portion of the dried air also called a purge gas from one desiccant chamber that is drying air to regenerate the desiccant in another chamber that has already removed moisture from the wet air earlier. The portion of dried air or purge gas is often diverted to a heater to elevate the temperature of the purge gas. Thereafter, the heated purge gas is moved to the other desiccant chamber to dry out and regenerate the saturated desiccant located therein.
These known regenerative gas drying devices typically use a dual chamber system in which wet gas is received through an inlet at the top of one of the chambers. As the wet gas migrates through the chamber, moisture is adsorbed by the desiccant thereby drying the gas. The majority of the dried gas is carried to a gas outlet thereby leaving the gas drying system. However, a small portion of the gas called purge gas is diverted to a transport pipe which carries the dry gas to a heater.
The purge gas is heated and transported to the other chamber which is operating to regenerate or dry out the previously adsorbed desiccant. The heated purge gas dries the saturated desiccant in the other chamber during the regeneration cycle. The high moisture air resulting from the drying of the saturated desiccant is removed from the other chamber at an opposite end from the end which receives the purge gas.
Once the desiccant in the first chamber drying the wet gas is sufficiently saturated during the air drying cycle and the desiccant in the other chamber is dried out during the regeneration cycle, the cycles are reversed by flipping diverter valves interposed between the two pressure chambers. The dry and heated purge gas received from the other chamber drying wet air is, in turn, used to dry and regenerate the saturated desiccant in the first chamber. These drying systems are cycled back and forth in this manner to continuously dry out the wet gases and regenerate desiccant.
Disadvantageously, many problems arise in employing such known gas drying systems. A significantly large percentage of the dried air must be used for purge in order to regenerate the saturated desiccant. This results in an inefficient use of the dried air since a high percentage of it must be used as purge to dry saturated desiccant instead of being used right away or collected, contained and sold for industrial purposes. Furthermore, the high percentage of the diverted dry air must be heated by heaters which utilize large quantities of energy and operate at very high temperatures. The high temperatures can precipitate fire hazards particularly when such heaters are in close proximity to oil lubricated compressors used in conjunction with these systems to pressurize the desiccant chambers.
Attempts have been made to dry material in a cylindrical receptacle by subjecting the material to electromagnetic waves. In U.S. Pat. No. 4,339,648 to Jean issued Jul. 13, 1982, an antenna extends the entire length of a single receptacle to provide radiation energy from top to bottom of the receptacle. Jean also shows a coiled antenna which extends along a helix inside the receptacle. Jean, however, is not used in a dual chamber regenerative gas drying system in which dry purge gas is inserted at one end of one chamber regenerating desiccant. Disadvantageously, the antenna of Jean extends the entire length of the chamber which inefficiently wastes radiant energy on areas which are relatively dry in regenerative gas drying systems and which do not necessarily need such radiant energy. Since the apparatus of Jean is not employed in a regenerative gas drying system, it does not concentrate the distribution of energy on areas within the chamber which require the most heat to regenerate saturated desiccant contained therein.
Attempts have further been made to transmit microwave energy into pressurized tanks in regenerative gas drying systems to heat gases adsorbed by desiccant materials contained therein. In U.S. Pat. No. 4,312,640 to Verrando issued Jan. 26, 1982, and U.S. Pat. No. 4,312,641 to Verrando issued Jan. 26, 1982, microwave energy is passed through microwave pressure windows and into tanks carrying sorbent or desiccant material. The microwaves are used to release and remove a polar gas adsorbed by sorbent or desiccant material in the tanks. The microwave energy is prevented from being sent into the tanks in response to the desorbtion of the moisture from the sorbent material. Purge gas is still moved through the desorbing desiccant until the moisture level of the chamber is adequately lowered.
In U.S. Pat. No. 4,322,394 to Mesey et. al. issued Mar. 30, 1982, microwave energy is used to dielectrically heat saturated solids of noncarbon adsorbents for the removal of adsorbed materials. The microwaves heat the adsorbents internally to bring the adsorbents to a temperature for desorbing some of the adsorbate in the absence of any activating or purge gas.
Disadvantageously, in these systems the distribution of the microwave energy within the pressurized tanks is limited. Furthermore, there is continued inefficient use of purge gas to aid in the drying cycle for regenerating desiccant contained therein. The microwave energy in such devices which is sent through pressure windows adjacent the tank enhances the ability of removal of the adsorbed material proximate to the pressure windows. However, since these known air drying systems do not sufficiently disperse the microwaves through concentrated areas of high saturation in the tank, the material adsorbed by the desiccant located away from the pressure windows does not get sufficiently energized by the microwaves to efficiently adsorb the adsorbate material. Thus, desorbtion of wet gas is achieved only at locations proximate to the pressurized windows while desiccant further away from the pressure windows does not receive effective and beneficial microwave energy for desorbtion. Additionally, such systems do not use microwave energy to ultimately heat dry gas which is inserted into the regenerating tank as purge.